Small diameter glass fibers are useful in a variety of applications including acoustical or thermal insulation materials. When these small diameter glass fibers are properly assembled into a lattice or web, commonly called a wool pack, glass fibers which individually lack strength or stiffness can be formed into a product which is quite strong. The glass fiber insulation which is produced is lightweight, highly compressible and resilient. For purposes of this patent specification, in using the terms "glass fibers" and "glass compositions", "glass" is intended to include any of the glassy forms of mineral materials, such as rock, slag and basalt, as well as traditional glasses.
The common prior art methods for producing glass fiber insulation products involve producing glass fibers from a rotary process. A single molten glass composition is forced through the orifices in the outer wall of a centrifuge or spinner, producing primarily straight glass fibers. The fibers are drawn downward by a blower, and conventional air knife and lapping techniques are typically used to disperse the veil. The binder required to bond the fibers into a wool product is sprayed onto the fibers as they are drawn downward. The fibers are then collected and formed into a wool pack. The wool pack is further processed into insulation products by heating in an oven, and mechanically shaping and cutting the wool pack.
Ideally, insulation products of glass fibers would have uniform spacing between fibers assembled in the lattice. Glass fiber insulation is basically a lattice which traps air between the fibers and prevents circulation of air to inhibit heat transfer. As well, the lattice also retards heat transfer by scattering thermal radiation. A more uniform spacing of fibers would maximize scattering and, therefore, have greater insulating capability.
In the production of wool insulating materials of glass fibers, it becomes necessary to use fibers that are relatively short to achieve desirable lattice properties. Known lapping techniques for dispersion of short fibers in a veil have provided acceptable, although not ideal fiber distribution. By contrast, long fibers tend to become entangled with each other, forming ropes or strings. For purposes of this patent specification, in using the terms "short fibers" and "long fibers" the term "short fibers" is intended to include fibers of approximately 2.54 centimeters (approximately 1 inch) and less, and "long fibers" are intended to include fibers longer than approximately 5.08 centimeters (approximately 2 inches).
Long fibers are more prone to entangle than short fibers, due, in part to their different aerodynamic properties, in addition to fiberizer throughput and geometry. Moreover, the longer they are, the more the long fibers tend to entangle. Conventional lapping techniques have failed to eliminate, and rather tend to enhance, formation of ropes and strings in veils of long or semi-continuous fibers. Even when undisturbed, veils of long fibers tend to form ropes and strings as the veil slows in its descent to the collection surface. Despite movement of the collection surface, long glass fibers (as do undisturbed veils of short fibers) tend to pile up into nonuniform packs of fibers, and unmanageable fiber accumulations. These nonuniform packs, characterized in part by roping and string formation, have long prevented significant commercial use of long fibers. The ropes of long fibers produce a commercially undesirable appearance and, more importantly, create deviation from the ideal uniform lattice and reduce the insulating abilities of the glass wool.
However, even short fibers that are straight form only a haphazard lattice, and some of the fibers lie bunched together. As a result, existing glass wool insulating materials continue to have significant non-uniformities in the distribution of fibers within the product. Thus, the ideal uniform lattice structure cannot be achieved.
A further problem presented by use of short straight fibers is the binder material necessarily added to the fibers to provide product integrity. Binder provides bonding at the fiber to fiber intersections in the lattice, but is expensive and has several environmental drawbacks. As most binders include organic compounds, great pains must be taken to process effluent from the production process to ameliorate the negative environmental impact of such compounds. Further, the binder must be cured with an oven, using additional energy and creating additional environmental cleanup costs. While long fibers display fiber to fiber entanglement even without binder, the nonuniformity of the resulting wool packs has long made them commercially undesirable.
Finally, in addition to the properties of uniformity and integrity, it is desirable for wool packs to exhibit recovery from compression. In the shipping and packaging of insulation products, high compressibility is preferred. It is desirable to compress the wool for shipping and then have it recover rapidly and reliably to the desired size. When the product is compressed, the binder holds firm at fiber to fiber intersections while the glass fibers themselves flex. If the stress upon the fiber increases due to excessive compression, the fiber breaks. Thus, current insulation products are limited in the amount of compression possible while still attaining adequate recovery.
Nonetheless, because long fibers are problematic in nearly all respects, commercial wool insulation products of glass fibers have long used only short straight fibers, despite the various drawbacks of short fibers in lattice non-uniformity, need for binder and related environmental concerns, and limited compressibility. Accordingly, the need remains for further improvements in wool insulation products to improve wool pack properties, reduce cost and eliminate environmental concerns.